Here is what the Intel and AMD platforms offer in terms of I/O
X99 Platform
Processor: 40 Gen3 lanes + 4 Gen3 lanes (w/ DMI extensions)
Chipset: 4 Gen3 lanes in / 8 Gen2 lanes out + USB + SATA
X299 Platform
Processor: 44 Gen3 lanes + 4 Gen3 lanes (w/ DMI extensions)
Chipset: 4 Gen3 lanes in / 24 Gen3 lanes out + USB + SATA
Z270 Platform
Processor: 16 Gen3 lanes + 4 Gen3 lanes (w/ DMI extensions)
Chipset: 4 Gen3 lanes in / 24 Gen3 lanes out + USB + SATA
X370 + Ryzen Platform
Processor: 16 Gen3 lanes + 4 Gen3 lanes (configurable as 2 SATA + 2 PCI-e, 2 SATA + x2 M.2, or x4 M.2) + 4 Gen3 lanes (to chipset) + USB
Chipset: 4 Gen3 lanes in / 4 Gen3 lanes out (configurable as 4 PCI-e lanes or 2 SATA Express) + 8 Gen2 lanes out + USB + SATA
X300 + Ryzen Platform
Processor: 16 Gen3 lanes + 4 Gen3 lanes (configurable as 2 SATA + 2 PCI-e, 2 SATA + x2 M.2, or x4 M.2) + 4 Gen3 lanes (to chipset) + USB
Chipset: 4 Gen3 lanes in / 4 Gen3 lanes out (configurable as 4 PCI-e lanes or 2 SATA Express)
Note that AMD has embedded I/O into the processors and this changes with the type of processor. As far as we know, all high-end Ryzen will have the same 24 Gen3 lanes + 4 USB 3.0, but the APU's will have a different I/O configuration with fewer PCI-e lanes, etc. The same AM4 socket is used for all AMD platforms.
Notice that the Z270 and X299 chipsets have the same output...it wouldn't surprise me is the chipset silicon was the same. Only the socket would be different between the two, but that won't stop substantial premiums being applied to the X299 boards.
All chipsets have 4 PCI-e Gen3 lanes bridging them to the processor. X300 essentially will be a pass-through, but all others are essentially fancy PCI-e switches with logic for USB, SATA, and other interfaces (TPM, etc.)